1. Field of the Invention
The present invention relates to a sheet-fed printing press, and more particularly a control mechanism for controlling associated operations of the sheet-fed printing press to mount a printing plate on a plate cylinder.
2. Discussion of the Background
According to a conventional sheet-fed printing press, a printing plate having a leading edge and a tail edge is wound around the outer circumference of a plate cylinder, and ink and dampening solution are fed to the printing plate for the sheet printing. The plate cylinder forms therein a recessed portion, in which a leading edge clamp (first clamp device) for clamping the leading edge of the printing plate and a tail edge clamp (second clamp device) for clamping the tail edge of the printing press are disposed.
The leading edge clamp includes a base part and a movable part to apply a clamping force onto the upper and lower surfaces of the leading edge of the printing plate. Similarly, the tail edge clamp includes a base part and a movable part to apply a clamping force onto the upper and lower surfaces of the tail edge of the printing plate. The tail edge clamp is also designed to move in a first direction to pull the printing plate into tensed state along a sheet feeding passage of the printing press, which passage extends around the outer circumference of the plate cylinder, and in a second direction to release the printing plate from the tensed state along the sheet feeding passage.
A printing plate pressing roller as a printing plate pressing device is disposed near the plate cylinder in such a manner as to be movable to and away from the outer circumference of the plate cylinder for timely pressing the printing plate against the outer circumference of the plate cylinder. An edge insertion device is also disposed near the plate cylinder for guiding the tail edge of the printing plate into the tail edge clamp.
In recent years, attempts have been continuously made to automatize the printing-plate feeding operation, printing-plate removing operation and/or any other associated operations. For example, in the printing-plate feeding operation for feeding the printing plate on the printing cylinder, an operator first inserts the leading edge of the printing plate into the leading edge clamp and then actuates the leading edge clamp to clamp the leading edge of the printing plate. After that, the printing press is automatically operated to perform the subsequent plate feeding actions in the following manner.
The plate cylinder starts to rotate in the forward direction with the leading edge of the printing plate clamped by the leading edge clamp. Along with the forward rotation of the plate cylinder, the printing plate pressing roller moves to the plate cylinder and then presses the printing plate against the outer circumference of the plate cylinder. With continuously pressing the printing plate by the pressing roller, the plate cylinder rotates in the forward direction to a predetermined angular position, so that the printing plate is wound around the plate cylinder and has its tail edge brought into contact with the edge insertion device. The plate cylinder stops its rotation once the tail edge contacts the edge insertion device.
The edge insertion device then guides the tail edge of the printing plate into the tail edge clamp, which then clamps the tail edge therein. At this moment, the printing plate with its leading and tail edges clamped by the respective clamps still does not have the entire length brought into a tight contact with the outer circumference of the plate cylinder. To achieve the tight contact throughout the entire length of the printing plate, the tail edge clamp is moved in the first direction by a predetermined distance, applying pulling force onto the printing plate, thereby bringing the same into tight contact with the outer circumference of the plate cylinder. A series of operations for feeding the printing plate are thus finished. Subsequent to this, the pressing roller is moved away from the plate cylinder, enabling the printing press to start the printing operation.
With respect to the size of the printing plate, a length of the printing plate along the rotational direction of the plate cylinder is usually limited to such a length as to enable both clamps to clamp the respective edges of the printing plate (standard-sized printing plate). However, the printing may sometimes be operated, using a printing plate having a post-card size or any other shorter size, whose both edges cannot reach the respective clamps and therefore tail edge cannot be clamped (shorter-sized printing plate). In such a printing operation without tail edge clamped, only the leading edge of the printing plate is clamped by the leading edge clamp during the printing operation due to the shortness of the length of the printing plate along the sheet-feeding passage.
According to the conventional printing press of the above type, even if the printing plate having a shorter length is fed on the plate cylinder, the tail edge clamp is unnecessarily actuated, and the plate feeding operation cannot be completed before the action of the tail edge clamp is completed, so that the operator must wait the completion of the action of the tail edge clamp. With such a problem there exists a demand for an improved printing press that is capable of shortening a printing plate feeding operation time.
Therefore, in consideration of solving the above problem it is an object of the present invention to provide an improved printing press that is capable of carrying out the printing press feeding operation in a reduced time period when the printing operation without tail edge clamped is to be carried out.
According to the present invention, there is provided a sheet-fed printing press that includes a plate cylinder, a first clamp device, a second clamp device, and a control device. The plate cylinder is rotatable in the forward direction and the reverse direction, and has an outer circumference around which a printing plate having a leading edge and a tail edge located opposite to each other is wound. The first clamp device is disposed on the plate cylinder for clamping the leading edge of the printing plate. The second clamp device is disposed on the plate cylinder for clamping the tail edge of the printing plate, and is movable in a first direction to pull the printing plate into tensed state and in a second direction to release the same from the tensed state. The control device is provided for controlling the printing press, so that the printing press is operable in a standard-sized printing plate feeding mode for feeding a printing plate having a standard size on the outer circumference of the plate cylinder and a shorter-sized printing plate feeding mode for feeding a printing plate having a shorter size than the standard size on the outer circumference of the plate cylinder.
According to the above arrangement, when the standard-sized printing plate feeding mode is selected, the control device controls the printing press so that the plate cylinder is rotated in the forward direction with the leading edge of the printing plate clamped by the first clamp device, thereby enabling the printing plate to be wound around the plate cylinder, and the second clamp device clamps the tail edge and is moved in the first direction. thereby pulling the printing plate into tensed state. Whereby, the printing plate is brought into tight contact with the outer circumference of the plate cylinder. Thus, the printing plate feeding operation is completed.
On the contrary, when the shorter-sized printing plate feeding mode is selected, the control device controls the printing press so that the plate cylinder is rotated in the forward direction with the leading edge of the printing plate clamped by the first clamp device. Whereby, the printing plate can be wound around the plate cylinder. Thus, the printing plate operation is completed without actuation of the second clamp member.
In the above arrangement, the standard-sized printing plate feeding mode is selected to wind around the plate cylinder the printing plate whose length is a standard size, enabling both clamps to respectively clamp the leading and tail edges. The shorter-sized printing plate feeding mode is selected to wind around the plate cylinder the printing plate whose length is not so long as to extend between both clamp devices.
With the above arrangement, the sheet-fed printing press of the present invention is operable in the shorter-sized printing plate feeding mode besides the standard-sized printing plate feeding mode, so that the operator can suitably select the plate feeding mode according to the size of the printing plate. Thus, the plate feeding operation time for the shorter-sized printing plate may be shortened.
A sheet-fed printing press may also be operable in a standard-sized printing plate removing mode and a shorter-sized printing plate removing mode. According to these operational modes, when the standard-sized printing plate removing mode is selected, the control device controls the printing press so that the plate cylinder is rotated in the reverse direction with the tail edge of the printing plate released from clamped engagement with the second clamp device. When the shorter-sized printing plate removing mode is selected, the control device controls the printing press so that the plate cylinder is rotated in the forward direction with the leading edge of the printing plate released from clamped engagement with the first clamp device.
In the above arrangement, the standard-sized printing plate removing mode is selected to remove from the plate cylinder the printing plate having a standard size with the leading and tail edges clamped by both clamp devices. The shorter-sized printing plate removing mode is selected to remove from the plate cylinder the printing plate having a shorter size than the standard size with only the leading edge clamped by the first clamp device.
When the standard-sized printing plate removing mode is selected, the operator can hold the released tail edge of the printing plate by hand, and remove the same away from the plate cylinder through the reverse rotation of the plate cylinder. When the shorter-sized printing plate removing mode is selected, the operator can hold the released leading edge of the printing plate by hand, and remove the same away from the plate cylinder through the forward rotation of the plate cylinder.
Where the printing press is operable in the shorter-sized printing plate removing mode besides the standard-sized printing plate removing mode, as described above, a suitable plate removing mode may be selected according to the size of the printing plate. Particularly in the shorter-sized printing plate removing mode, the control device controls the plate cylinder to forwardly rotate. This forward rotation prevents the printing plate from being accidentally removed from the plate cylinder and then curling up, so that the printing plate can removed from the plate cylinder in easy and secured manner.